(1) Field of the Invention
The present invention relates to a vinyl chloride polymer resin composition having excellent processability and flowability, which comprises a vinyl chloride polymer having a low degree of polymerization.
(2) Description of the Related Art
A vinyl chloride polymer resin has excellent chemical and physical properties but, as is well known, this resin has poor heat stability, impact resistance and processability. Various methods have been proposed for overcoming these defects. More specifically, various heat stabilizers have been developed for improving the heat stability and various impact modifiers have been developed for improving the impact resistance. These additives have been used by incorporation into vinyl chloride polymer resins. As an agent for improving the processability, there has been proposed a high-molecular weight acrylic polymer processing aid. Namely, the incorporation of a small amount of this processing aid in a vinyl chloride polymer resin can improve the processability of the vinyl chloride polymer resin, for such processes as calendering, vacuum forming or injection molding (refer to Japanese Examined Patent Publication No. 40-5311).
Where a vinyl chloride polymer resin composition is prepared by incorporating this high-molecular weight acrylic polymer processing aid into a commercially available vinyl chloride polymer resin having a high degree of polymerization, the melt viscosity is drastically increased, even though the amount of the processing aid added is small, and the kneading lead in a molding machine is extremely increased. Moreover, since the resin molding temperature must be elevated, the resin is thermally degraded and it is difficult to continue the processing for a long time. The above problem becomes prominent, especially when the processing temperature is high and the processing is performed at a high speed. As means for overcoming this disadvantage, there may be considered a method for improving the flowability by adding a liquid substance such as a plasticizer, but here reduction of the physical properties and processability cannot be avoided.
Also in the field of vinyl chloride polymer resins having a low degree of polymerization, development of a product having a good processability is desired but a satisfactory product has not been developed.